An NVM which is able to continually store information even when the supply of electricity is removed from the device containing the NVM cells. Recently, the most widespread used NVMs are charge trap flash (CTF) memory devices. However, as semiconductor features shrink in size and pitch, the CTF memory devices have its physical limitation of operation. In order to solve the problems, a resistance switching memory device, such as a resistive random-access memory (ReRAM) device is thus provided.
ReRAM devices that apply difference of resistance within the resistance switching memory cells thereof to implementing the erase/program operation have advantages in terms of cell area, device density, power consumption, programming/erasing speed, and the like over other FLASH memory devices, and thus have become a most promising candidate for leading products in the future memory market.
The programming of a ReRAM device typically includes steps as follows: A programming pulse is first applied to at least one resistance switching memory cell selected from the ReRAM device to make the resistance distribution state of the resistance switching memory cell shift from a first resistance distribution state (e.g. a low resistance distribution state) to a second resistance distribution state (e.g. a high resistance distribution state). A verification process is then performed to determine whether the resistance distribution state of the resistance switching memory cell has shift to the second resistance distribution state. In order to implement the verification process, a proper resistance window for identifying the two different resistance distribution states is required.
Therefore, there is a need of providing an improved method for operating an NVM device for identifying the two different resistance distribution states with a proper resistance window.